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(up to speed)
Irrigation, agronomics
and playability
Thomas A. Nikolai, Ph.D.
nikolait@msu.edu
To summarize,
most golfers
incorrectly believe
that withholding
irrigation increases
the speed of the
green; however, that
is only true if the
greens are allowed
to turn brown. At
the other extreme,
overwatering leads
to soft greens and
numerous longterm turfgrass health
problems.
130
GOLF COURSE MANAGEMENT 01.14
"Proper turf irrigation is the most diffcult
day-to-day agronomic decision the golf course
superintendent makes" is the sentence James B.
Beard, Ph.D., used to open Chapter 9 of "Turf
Management for Golf Courses."
That sentence is remarkable in its bluntness
considering Dr. Beard is a pre-eminent turfgrass scientist, and one trait all scientists have
in common is the desire to leave wiggle room
for unexplained variables. Having said that, I
have tested Dr. Beard's boldness at numerous
conferences by displaying the quote on a PowerPoint slide and asking if anyone disagrees
with the statement. To date, no superintendent
has ever challenged it.
Why is it so hard to make daily decisions
about irrigation? Obviously, a lot of factors
are involved, but it comes down to the fact
that there is no simple method to measure the
amount of plant-available water in the root
zone. Now I am certain that "Soils" was your
favorite class in college, but in case you have
forgotten, plant-available water is the amount
of water between feld capacity and wilting
point and it is different in every soil. Addition
of irrigation water above feld capacity results
in water being pulled by gravity below the root
zone — a saturated condition that wastes water
and diminishes playing quality.
A study performed by Rod Tocco at Michigan State University yielded results that demonstrate the interaction of irrigation on agronomics and playability. For three years, water
was replenished on push-up research putting
greens at evapotranspiration (ET) levels of 30
percent, 60 percent or 90 percent. In the frst
two years of the study, there were suffcient and
timely rain events resulting in no visual difference between any of the irrigation treatments.
The third year was hot and dry, and the greens
that received 30 percent ET water replenishment displayed signs of localized dry spot. It
was not until these greens turned brown from
lack of water that there were differences in
green speed among irrigation treatments.
Does that mean that the amount of irrigation applied on the putting surface has no
impact on playability? No, not at all because
irrigation directly affects the frmness or shot
acceptance of the green.
Now let's return to Tocco's results and consider irrigation quantity and its impact on shot
acceptance. In the study, greens receiving 90
percent ET water replenishment consistently
had the least amount of microbial activity.
The lack of microbial activity suggests that
those greens had less oxygen in the root zone,
which is a result of overwatering. Long-term
decreased microbial activity results in thatch
accumulation, deeper ball marks, footprinting,
scalping and diminished turfgrass quality and
customer satisfaction.
To summarize, most golfers incorrectly
believe that withholding irrigation increases
the speed of the green; however, that is only
true if the greens are allowed to turn brown.
At the other extreme, overwatering leads to
soft greens and numerous long-term turfgrass
health problems. Defning the proper amount
of irrigation to replenish has always been diffcult, but fortunately technology has refned
time domain refectometry (TDR), allowing
superintendents to make more informed decisions on how much water to replenish on a
daily basis.
TDR moisture sensors (both hand-held and
in ground) are the best tools to date for simple volumetric moisture content results. Given
time (one year or so) and good record keeping,
a superintendent can estimate the volumetric
moisture content that correlates with the wilting point and feld capacity of his root zone(s).
When this is accomplished, it becomes possible to irrigate within plant-available water
parameters. This saves water, makes turfgrass
healthier and improves playing conditions,
which increases customer satisfaction. Putting
this all together, it seems logical that golfers
and superintendents can come together and
embrace TDR technology. I don't think Dr.
Beard would mind if he had to rewrite his frst
sentence from Chapter 9.
Thomas A. Nikolai, Ph.D., is the turfgrass academic specialist at Michigan State University in East Lansing, Mich.,
and a frequent GCSAA educator.